While there is no one definition of mansions by size, a good rule of thumb is 5,000 square feet. The square footage varies by area, as a 5,000-square-foot house in Manhattan is considered a mansion, but in some suburbs it's not. Normally, mansions indicate greater grandeur than the norm.
Mansions usually contain one or more rooms for entertainment purposes such as a home theater and a game room. They usually include lavish outdoor spaces such as courtyards, pools and verandas. Mansions are sometimes not single standing houses but a whole compound of buildings, such as the Kennedy Compound in Hyannis Port, Mass.